1. Field of the Invention
The present invention relates to a cap assembly of a battery, and more particularly, to a cap assembly of a battery having ventilation rubber in which pressure applied to the ventilation rubber is dispersed by improving the shape of a cap cover, to maintain restoring force of the ventilation rubber under conditions in which the battery is repeatedly charged and discharged.
2. Description of the Related Art
In general, batteries for supplying direct current voltage are divided into dry cells used for various electric devices, and storage batteries used for automobiles and uninterruptible power systems.
FIG. 1 is a sectional view of the internal structure of a conventional battery.
Referring to FIG. 1, the battery is comprised of a cylindrical case 11 and a roll structure in the case 11. That is, positive plates 12 and negative plates 13 of rectangular thin plates having a predetermined width and length are alternately arranged around a core (not shown) to form the roll structure. A separator 14 located between the positive plate 12 and negative plate 13 insulates the two plates 12 and 13.
Also, upper and lower rings 15 and 16 installed on upper and lower edges of the roll structure fix and support the plates 12 and 13. A gasket 20, and a cap 18 and a cap cover 19 each supported by the gasket 20 are installed on the upper ring 15. Ventilation rubber 17 is interposed between the cap 18 and the cap cover 19.
In the above-described battery, excessive charge generates gas, which causes a rapid increase in the internal pressure of the battery. Here, a cap assembly is for preventing explosion of the case 11 due to the internal pressure increase.
FIGS. 2A and 2B are respectively a vertical cross-sectional view and an end view of a crimped cap assembly, and FIGS. 3A and 3B are respectively a vertical cross-sectional view and an end view of a welded cap assembly.
Referring to FIGS. 2A and 2B, a cap assembly 20 of a battery is comprised of a cap 21, a cap cover 23, and ventilation rubber 22 interposed between the cap 21 and the cap cover 23. The ventilation rubber 22 closes a ventilation hole 24 in the center of the cap cover 23.
Referring to FIGS. 3A and 3B, a mechanism of the cap assembly for preventing an increase in the internal pressure of the battery will be described as follows.
When internal pressure in the case increases beyond a predetermined level due to the gas generated during repeated charges and discharges, pressure is applied toward a ventilation hole 34 in the center of the cap cover 33. Accordingly, ventilation rubber 32 closing the ventilation hole 34 moves upward and departs from the cap cover 33. As a result, the ventilation rubber 32 opens to emit gas outward.
However, during repeated charges and discharges, the ventilation rubber repeatedly contracts and expands, so that its restoring force is deteriorated, which causes gas and electrolyte leakage through a gap between the cap cover and the ventilation rubber, so that the life span of the battery is reduced.